Generally, a broadband wireless access system supports an idle mode and a sleep mode to reduce power consumption of a mobile station (MS).
In the sleep mode, the mobile station repeats sleep intervals and listening intervals. Namely, the mobile station, which does not perform a communication with a base station during the sleep interval, receives a traffic notification message (MOB-TRF-IND) from the base station once the listening interval begins. The mobile station then may acknowledge whether there is downlink traffic to be transmitted to the mobile from the base station using the received traffic notification message (MOB-TRF-IND). If the mobile station acknowledges there is the downlink traffic to be transmitted to the mobile station, the mobile station terminates the idle mode and then enters a normal mode. Meanwhile, if the mobile station acknowledges there is no downlink traffic to be transmitted to the mobile station, the mobile station does not perform the communication with the base station during the sleep interval. Hence, the mobile station in the sleep mode repeats the sleep and listening intervals, thereby reducing its power consumption.
Meanwhile, in the idle mode, the mobile station updates validity of the idle mode by receiving a paging message (MOB_PAG-ADV) each paging cycle. Namely, the mobile station, which communicates with the base station during the interval for receiving the paging message, can save power consumption. Unlike the mobile station in the sleep mode, the mobile station in the idle mode can move away into an area of another base station without performing handover within the same paging zone. Hence, the mobile station avoids power consumption caused by handover procedure.
A connection establishment using a mobile IP is explained as follows.
First of all, it is assumed that an IP mostly used in Internet environment can uniquely identify an access point of a certain node (e.g., host, router, etc.) using an IP address. In this case, a node should be located within a network including its IP address for receiving a datagram transmitted from a corresponding node. If the node fails to be located within the network including its IP address, the datagram cannot be transmitted to the node.
If a random node attempts to change its access point while keeping a communication, one of the two following methods should be adopted.
Firstly, the node changes its IP address each time the access point changes.
Secondly, an address of a moved host should be transmitted Internet overall.
Yet, the above two methods have problems.
According to the first method, it is difficult to maintain a connection between a transport layer and its higher layer when a location of the node is changed.
Assuming that the number of mobile nodes increases later, it is difficult to substantially adopt the second method.
Hence, a more extendible technology is needed to support mobility of node in Internet. And, a mobile IP is a solution to support the mobility.
In the mobile IP, a foreign agent (hereinafter abbreviated FA) or a home agent (hereinafter abbreviated HA) informs that a mobile station is located within which agent area using an agent advertisement message.
However, in the related art, not receiving the downlink data, the mobile station in the idle or sleep mode is unable to receive the agent advertisement message. So, the mobile station failing in receiving the agent advertisement message for a predetermined time terminates the idle or sleep mode and then enters the normal mode to transmit uplink information to search an HA or FA. Hence, it is unable to sufficiently take advantage of the idle or sleep mode.